Star polymers, and their preparation

ABSTRACT

Star polymers obtainable by polymerization of vinylaromatic monomers with a branching monomer unit containing at least two vinylaromatic functional radicals in the presence of a catalyst obtainable from A) a transition-metal complex from sub-group II to VIII, B) a cation-forming agent and C), if desired, an aluminum compound.

The present application is a divisional of U.S. Ser. No. 09/242,731,filed Feb. 22, 1999 which was filed as PCT/EP 97/04432, filed on Aug.13, 1997.

DESCRIPTION

The present invention relates to star polymers obtainable bypolymerization of vinylaromatic monomers with a branching monomer unitcontaining at least two vinylaromatic functional radicals in thepresence of a catalyst obtainable from A) a transition-metal complexfrom sub-group II to VIII, B) a cation-forming agent and C), if desired,an aluminum compound.

The present invention furthermore relates to a process for thepreparation of these star polymers and to their use for the productionof fibers, films and moldings, in particular injection molding materials[sic], and the resultant fibers, films and moldings.

Owing to its crystallinity, syndiotactic polystyrene has a very highmelting point of about 270° C., high rigidity, tensile strength anddimensional stability, a low dielectric constant and high chemicalsresistance. The mechanical property profile is retained even at abovethe glass transition temperature. The preparation of syndiotacticpolystyrene in the presence of metallocene catalyst systems isdisclosed, for example, in EP-A-210 615.

The low toughness and poor solubility, even in chlorinated solvents, andthe low compatibility in blends with thermoplastics, for example PS, PB,PMMA, PE, PP, EP, PA6, PA66, PET, PBT, ABS, ASA etc., aredisadvantageous. Furthermore, crystallization of the syndiotacticpolystyrene frequently occurs from a conversion of as low as around 10%.

EP-A-572 990 describes metallocene-catalyzed copolymers of styrene andethylene which have improved compatibility and high elasticity. However,these copolymers do not have the high stereotacticity and therefore donot achieve the high-temperature properties of syndiotactic polystyrene.

Copolymers of styrene and divinylbenzene are described in EP-A-311 099and EP-A-490 269. Under the reaction conditions, only one vinyl group ofthe divinylbenzene reacts. The remaining vinyl groups are used forgrafting reactions or crosslinked by means of free radicals onconditioning at about 230° C., molecular weights of from 1,000,000 to6,000,000 only being obtained after this crosslinking reaction.

Star polymers belong to the class of the branched polymers (Falbe, RömppChemie Lexikon, Georg Thieme Verlag, 9th Edition, Stuttgart 1992, page4304). They are usually prepared by polymerization of monomers withpolyfunctional initiators, polyaddition of, for example, epoxides ontopolyhydric alcohols or coupling of pre-prepared polymers, for example Lipolystyrene, onto a center, for example silicon tetrachloride.

It is an object of the present invention to provide star polymers madefrom vinylaromatic monomers, which polymers simultaneously have highmolecular weight and low melt viscosities, and a high end-groupfunctionality for graft reactions, crosslinking reactions and otherpolymer-analogous reactions. Furthermore, the star polymers should havean essentially syndiotactic structure, ie. have a syndiotacticity ofgreater than 30%, in particular greater than 60%.

We have found that this object is achieved by the star polymers definedat the outset containing the branching monomer units containing at leasttwo vinylaromatic functional radicals.

These polymers have high molecular weights of from 500,000 to 10,000,000at the same time as low melt viscosities of less than 500 ml/10 min at290° C. and a weight of 10 kg, and have significantly greater end-groupfunctionalities compared with syndiotactic styrene of comparablemolecular weight. In general, the endgroup functionality is greater than0.5 mol %, particularly preferably greater than 0.8 mol %.

These properties can be modified within a broad range by means of themolar ratio between the vinylaromatic monomer and branching monomerunits according to the invention. The molar ratio between vinylaromaticmonomers and the branching monomer unit is generally from 10,000,000:1to 10:1.

The novel star polymers have a syndiotacticity greater than 60%, ingeneral greater than 90%.

The branching monomers can, according to the invention, be compounds ofthe formula I

where

R^(a) is hydrogen, halogen or an inert organic radical having up to 20carbon atoms, where, in a case where p≧2, the two radicals R^(a) may beidentical or different and can, together with the metal atom to whichthey are bonded, form a 3- to 8-membered ring, and R^(a) may furthermorebe a conventional complex ligand if M is a transition metal;

R^(b) is hydrogen, C1-C₄-alkyl or phenyl;

R^(c) is hydrogen, C₁-C₄-alkyl, phenyl, chlorine or an unsaturatedhydrocarbon radical having 2 to 6 carbon atoms;

M is C, Si, Ge, Sn, B, Al, Ga, N, P, Sb, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,W, Mn, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Zn or Cd; p1 n is 2-6;

m is 0-20; and

p is 0-4;

with the proviso that the sum n+p corresponds to the valence of M.

These monomers can be obtained, for example, via the Grignard compoundsof chloro(alkyl)styrenes with the corresponding carbon, metal ortransition-metal compounds, for example the halogen compounds. Suchreactions have been described, for example, for the case where M issilicon, germanium or tin in K. Nakanishi, J. Chem. Soc. Perkin Trans.I, 1990, page 3362.

Particular preference is given to branching monomer units of the formulaI in which M is carbon, silicon, germanium, tin or titanium, since theyare readily accessible. The index m is preferably from 0 to 8,particularly preferably from 0 to 4.

The present invention also relates to the novel titanium-containingmonomers of the formula Ia

and in particular the titanium compound of the formula Ib

where R^(a), R^(b), R^(c), m, n and p are as defined above.

The inert organic radicals R^(a) are of no great significance for theprocess. Rather, they serve merely to saturate the free valences on Mand can be selected in accordance with ready availability. For example,aliphatic, cycloaliphatic, aryl, heteroaryl or aralkyl radicals aresuitable. Examples of aliphatic radicals are alkyl, alkoxy, alkenyl andalkynyl radicals having, for example, from 1 to 2 or 20 carbon atoms.Examples of cycloaliphatic radicals are cycloalkyl radicals having 3 to8 carbon atoms. A methylene group in the alkyl or cycloalkyl radicalscan also be replaced by an ether oxygen atom. Examples of aryl radicalsare phenyl and naphthyl radicals, in which two phenyl groups can also belinked to one another via an oxygen atom. Examples of aralkyl radicalsare those having 7 to 20 carbon atoms produced by combining a phenylradical with an alkyl radical. Examples of heteroaryl radicals arepyridyl, pyrimidyl and furyl radicals. These radicals may also befurther substituted, for example by alkyl, alkoxy, halogen, such asfluorine, chlorine or bromine, cyano, nitro, epoxy, carbonyl, estergroups, amides, etc. It is also possible for two of the radicals R^(a),together with the atom M, to form a 3- to 6-membered ring, for exampleby two radicals R^(a) forming an alkylene chain, in which one or moreCH₂ groups may also be replaced by ether oxygen atoms.

If M is a transition metal, R^(a) can also be a conventional σ- orπ-bonded complex ligand, such as ethylene, allyl, butadiene,cyclopentadiene, mono- or polysubstituted cyclopentadienes, such asmethylcyclopentadiene or pentamethylcyclopentadiene, benzene,cyclohexadiene, cycloheptatriene, cycloheptadiene, cyclooctatetraene,cyclooctatriene, cyclooctadiene, carbonyl, oxalato, cyano, isonitrile,fulminato-C, fulminato-O, cyanato, dinitrogen, ethyelenediamine,diethylenetriamine, triethylenetetramine, ethylenediamine tetraacetate,nitrosyl, nitro, isocyano, pyridine, α,α-dipyridyl, trifluorophosphine,phosphine, diphosphine, arsine or acetylacetonato.

R^(b) is particularly preferably hydrogen or methyl. R^(c) is hydrogen,C₁-C₄-alkyl, such as methyl, ethyl, propyl, isopropyl, n-butyl orbutylisomers, phenyl, chlorine or an unsaturated hydrocarbon radicalhaving 2 to 6 carbon atoms, such as vinyl, allyl, methallyl, butenyl orpentenyl.

Particularly suitable vinylaromatic compounds are those of the formulaII

where

R¹ is hydrogen or C₁- to C₄-alkyl,

R² to R⁶, independently of one another, are hydrogen, C₁- to C₁₂-alkyl,C₆- to C₁₈-aryl, or halogen, or two adjacent radicals together are acyclic group having 4 to 15 carbon atoms.

Preference is given to vinylaromatic compounds of the formula II where

R¹ is hydrogen, and

R² to R⁶ are hydrogen, C₁- to C₄-alkyl, chlorine or phenyl, or twoadjacent radicals together are a cyclic group having 4 to 12 carbonatoms, so that compounds of the formula II are, for example, naphthalenederivatives or anthracene derivatives.

Examples of preferred compounds of this type are the following:

styrene, p-methylstyrene, p-chlorostyrene, 2,4-dimethylstyrene,4-vinylbiphenyl, 2-vinylnaphthalene and 9-vinylanthracene.

It is also possible to use mixtures of different vinylaromaticcompounds, where one component may also carry further hydrocarbonradicals, such as vinyl groups, allyl groups, methallyl groups, butenylgroups or pentenyl groups, preferably vinyl groups, on the phenyl ring.However, it is preferred to use only one vinylaromatic compound.

Particularly preferred vinylaromatic compounds are styrene andp-methylstyrene.

The preparation of vinylaromatic compounds of the formula II is knownper se and is described, for example, in Beilstein U.S Pat. Nos.5,367,474, and 485.

The catalyst component A) used in accordance with the invention is atransition-metal complex from sub-group II to VIII, preferably fromsub-group III to VIII. Very particular preference is given to complexesof the metals titanium, zirconium and hafnium.

If the branching monomer unit of the formula I already contains attransition metal M, in particular titanium, it can, depending on theconcentration used, also be used simultaneously as catalyst component Ain addition to its function as branching unit.

The catalyst component A) is preferably a metallocene complex,particularly preferably of the formula III

where

R⁷ to R¹¹ are hydrogen, C₁- to C₁₀-alkyl, 5- to 7-membered cycloalkyl,which may itself carry C₁- to C₆-alkyl groups as substituents, C₆- toC₁₅-aryl or arylalkyl, it also being possible for two adjacent radicalstogether to form a cyclic group having 4 to 15 carbon atoms, orSi(R¹²)₃, where

R¹² is C₁- to C₁₀-alkyl, C₆- to C₁₅-aryl or C₃- to C₁₀-cyclo-alkyl,

M is a metal from sub-group III to VI of the Periodic Table of theElements or a metal from the lanthanide series,

Z¹ to Z⁵ are hydrogen, halogen, C₁- to C₁₀-alkyl, C₆- to C₁₅-aryl, C₁-to C₁₀-alkoxy or C₁- to C₁₅-aryloxy, and

z₁ to Z₅ are 0, 1, 2, 3, 4 or 5, where the sum Z₁+Z₂+Z₃+Z₄+Z₅corresponds to the valence of M minus 1.

Particularly preferred metallocene complexes of the formula III arethose in which

M is a metal from sub-group IV of the Periodic Table of the Elements,ie. titanium, zirconium or hafnium, in particular titanium, and

Z¹ to Z⁵ are C₁- to C₁₀-alkyl, C₁- to C₁₀-alkoxy or halogen.

Examples of preferred metallocene complexes of this type are thefollowing:

Pentamethylcyclopentadienyltitanium trichloride,

pentamethylcyclopentadienyltrimethyltitanium and

pentamethylcyclopentadienyltrimethoxytitanium.

It is also possible to use metallocene complexes as described in EP-A584 646.

Mixtures of different metallocene complexes can also be used.

These complex compounds can be synthesized by methods known per se,preference being given to reaction of the appropriately substitutedcyclic hydrocarbon anions with halides of titanium, zirconium, hafnium,vanadium, niobium or tantalum.

Examples of appropriate preparation processes are described, inter alia,in Journal of Organometallic Chemistry, 369 (1989), 359-370.

Suitable metallocenium ion-forming compounds B) in the catalyst systemare open-chain or cyclic aluminoxane compounds, for example of theformula IV or V

where R¹³ is C₁- to C₄-alkyl, preferably methyl or ethyl, and k is aninteger from 5 to 30, preferably from 10 to 25.

These oligomeric aluminoxane compounds are usually prepared by reactinga solution of trialkylaluminum with water, as described, inter alia, inEP-A 284 708 and U.S. Pat. No. 4,794,096.

In general, the oligomeric aluminoxane compounds are obtained as amixture of both linear and cyclic chain molecules of various lengths, sothat k can be regarded as a mean value. The aluminoxane compounds canalso be in the form of a mixture with other alkyl metal compounds,preferably alkylaluminum compounds.

It has proven advantageous to use the metallocene complexes and theoligomeric aluminoxane compounds in such amounts that the atomic ratiobetween aluminum from the oligomeric aluminoxane compound and thetransition metal from the metallocene complex is in the range from 10:1to 10⁶:1, in particular in the range from 10:1 to 10⁴:1.

The metallocenium ion forming compound B) can also be a coordinationcomplex compound taken from the group consisting of strong, neutralLewis acids, ionic compounds with Lewis-acid cations and ionic compoundswith Brbnsted acids as cations.

The strong, neutral Lewis acids are preferably compounds of the formulaVI

M¹X¹X²X³  (VI)

where

M¹ is an element from main group III of the Periodic Table, inparticular B, Al or Ga, preferably B,

X¹, X² and X³ are hydrogen, C₁- to C₁₀-alkyl, C6- to C₁₅-aryl,alkylaryl, arylalkyl, haloalkyl or haloaryl, each having 1 to 10 carbonatoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical,or fluorine, chlorine, bromine or iodine, in particular haloaryls,preferably pentafluorophenyl.

Particular preference is given to compounds of the formula VI, in whichX¹, X² and X³ are identical, preferably tris(pentafluorophenyl)borane.These compounds and processes for their preparation are known per se andare described, for example, in WO 93/3067.

Suitable ionic compounds with Lewis-acid cations are compounds of theformula VII

[(Y^(a+))Q₁Q₂ . . . Q_(z)]^(d+)  (VII)

where

Y is an element from main group I to VI or sub-group I to VIII of thePeriodic Table,

Q₁ to Q_(z) are radicals with a single negative charge, such as C₁- toC₂₈-alkyl, C₆- to C₁₅-aryl, alkylaryl, arylalkyl, haloalkyl, andhaloaryl, each having 6 to 20 carbon atoms in the aryl radical and 1 to28 carbon atoms in the alkyl radical, C₁- to C₁₀-cycloalkyl, which isunsubstituted or substituted by C₁- to C₁₀-alkyl, or are halogen, C₁- toC₂₈-alkoxy, C₆- to C₁₅-aryloxy, silyl- or mercaptyl groups,

a is an integer from 1 to 6,

z is an integer from 0 to 5, and

d is the difference a−z, but where d is greater than or equal to 1.

Particularly suitable are carbonium cations, oxonium cations, sulfoniumcations and cationic transition-metal complexes. Particular mentionshould be made of the triphenylmethyl cation, the silver cation and the1,1′-dimethylferrocenyl cation.

They preferably have non-coordinating counterions, in particular boroncompounds, as also mentioned in the WO 91/09882, preferablytetrakis(pentafluorophenyl) borate.

Ionic compounds with Bronsted acids as cations and preferably likewisenon-coordinating counterions are mentioned in WO 93/3067; the preferredcation is N,N-dimethylanilinium.

It has proven particularly suitable if the molar ratio between boronfrom the metallocenium ion forming compound and transition metal fromthe metallocene complex is in the range from 0.1:1 to 10:1, inparticular in the range from 1:1 to 5:1.

The catalyst system employed in the novel process can contain analuminum compound as component C), for example of the formula VIII

AlR¹⁴R¹⁵R¹⁶  (VIII),

where

R¹⁴ to R¹⁶ are hydrogen, fluorine, chlorine, bromine, iodine or C₁- toC₁₂-alkyl, preferably C_(1- to C) ₈-alkyl.

The radicals R¹⁴ and R¹⁵ are preferably identical C₁-C₆-alkyl radicals,such as methyl, ethyl, isobutyl or n-hexyl; R¹⁶ is preferably hydrogen.

Component C) is preferably present in the catalyst system in an amountfrom 1:2000 to 1:1, in particular from 1:800 to 1:10 (molar ratiobetween transition metal from III and Al from VIII).

The solvent used for the metallocene complex is usually an aromatichydrocarbon, preferably having 6 to 20 carbon atoms, in particularxylene, toluene, ethylbenzene, or a mixture thereof.

The metallocene complexes may if desired be supported.

Examples of suitable support materials are silica gels, preferably thoseof the formula SiO₂.bAl₂O₃, in which b is a number in the range from 0to 2, preferably from 0 to 0.5; ie. essentially aluminosilicates orsilicon dioxide. The supports preferably have a particle diameter in therange from 1 to 200 μm, in particular from 30 to 80 μm. Such productsare commercially available, for example as Silica Gel 332 from Grace.

Other supports include finely divided polyolefins, for example finelydivided polypropylene or polyethylene, but also polyethylene glycol,polybutylene terephthalate, polyethylene terephthalate, polyvinylalcohol, polystyrene, syndiotactic polystyrene, polybutadiene,polycarbonates or copolymers thereof.

The molar ratio between transition-metal catalyst A) and vinylaromaticmonomer is generally from 1:1000 to 1:10,000,000, but preferably from1:2000 to 1:1,000,000.

The present invention furthermore provides a process for the preparationof novel star polymers which can be carried out by observing the processconditions mentioned. A particular embodiment of the process comprisesusing a c o-rotating, tightly meshing and thus self-cleaning twin-screwextruder, preferably is one step.

The reaction temperature is generally from −80 to 150° C., preferablyfrom 0 to 120° C. However, it is also possible to apply a temnperaturegradient from 0 to 120° C. to the reaction tube via heatable jackets.

The extruder can consist of a plurality of individual zones which can beheld at different temperatures.

The outer diameter of the corotating, preferably double-flightedcompounding and conveying elements of the twin-screw extruder ispreferably in the range from 25 to 70 mm, in particular from 30 to 58mm.

The free space between the extruder barrel and the screw element is inthe range from 0.2 to 0.8 mm, in particular from 0.3 to 0.5 mm.

The screw speed can be in the range from 3 to 500 revolutions perminute, preferably from 5 to 30 revolutions per minute.

The mean residence time in the extruder can be from 0.1 to 240 minutes,preferably from 2 to 20 minutes.

The mean residence time in the extruder can be regulated via the numberof barrel blocks, which is preferably in the range from 6 to 20, inparticular from 8 to 12, but particularly preferably 10, backventingtaking place in the first block, the starting materials being meteredinto the second block, the reaction taking place in blocks 3 to 8,blocks 9 and 10 being heated to different temperatures if desired, anddischarge taking place in block 10.

The process is preferably carried out in such a way that thevinylaromatic compound, the branching monomer unit, the metalloceniumion-forming compound B) and, if used, the aluminum compound C) are mixedunder an inert-gas atmosphere and fed to the first extruder barrelblock. In parallel, a solution or suspension of the transition-metalcomplex (A) can likewise be fed to the first block (zone).

Solvents and suspending media which may be mentioned are cyclic andacyclic hydrocarbons, such as butanes, pentanes, hexanes and heptanes,furthermore aromatic hydrocarbons, such as benzene, toluene andethylbenzene, and oxygen-containing hydrocarbons, such astetrahydrofuran, halogen-containing hydrocarbons, such asdichloromethane, and nitrogen-containing hydrocarbons, such asN-methylpiperidine, and mixtures thereof.

The amount metered in is preferably selected so that from 500 to 2000g/h of the mixture of vinylaromatic compound, component B) and, if used,component C) are fed in along with from 100 to 200 cm³/h of the solutionor suspension of the metal complex.

The polymerization is preferably carried out in the vinylaromaticcompound as reaction medium, ie. in bulk.

The process is technically simple to carry out, high conversions areachieved, and the risk of sticking or blockage of the extruder outletapertures is low.

A further preferred embodiment comprises activating the reaction mixtureof the vinylaromatic monomers, the branching monomer unit and thecatalyst system consisting of A) a transition-metal complex fromsub-group II to VIII, B) a cation-forming agent and C), if desired, analuminum compound, by premixing and subsequently polymerizing themixture in a mixer/compounder.

The premixing is preferably carried out at a temperature at which thereaction mixture is still liquid and the polymerization does notcommence. Depending on the components used for the reaction mixture,this temperature is in the range from −30 to +140° C., preferably from 0to 70° C., particularly preferably from 15 to 30° C. Furthermore, in thecase of the novel activation, the premixing should preferably be carriedout in such a way that the residence time and temperature are selectedso that there is no damage to the catalyst, in spite of mixingsufficient for activation, and the polymerization reaction does notcommence.

The activation by premixing the reaction mixture is advantageouslycarried out shortly or immediately before the polymerization reaction.The time between activation by premixing and polymerization is from 0 to60 minutes, especially from 0.01 to 45 minutes, and particularlypreferably from 0.1 to 30 minutes, it being preferred for the premixingto be carried out essentially without a reaction commencing.

The process is advantageously carried out without a solvent. In aparticularly preferred embodiment of the process, the monomers employedinitially act as solvent. In addition, it is advantageous to carry outthe process in an inert-gas atmosphere, for example comprising nitrogenor argon, if possible with exclusion of moisture. It is also possible tometer hydrogen into the inert-gas stream.

The premixing is preferably carried out in such a way that no reactiontakes place. It is furthermore advantageous that polymers are obtainedin such a way that they can be processed further, preferably extruded,essentially immediately after the polymerization. This is preferably thecase if the polymerization process is carried out to high yields and thepolymer accordingly has a low residual monomer content of below 10% byweight, preferably below 5% by weight, particularly preferably below 3%by weight, based on the weight of the polymer. The residual monomercontent remaining in the polymer can be removed, for example, byevaporation or by applying a vacuum. The novel process is preferablycarried out in a mixing/compounding reactor with a downstream extruderwithout further work-up steps, for example removal of relatively largeamounts of monomer, which are produced, in particular, at lowconversions, by distillation, being necessary. The process thus permitsfurther processing of the polymer essentially immediately after itspreparation.

The resultant star polymers having syndiotactic chain branches and highmolecular weights in combination with low melt viscosity are suitablefor the production of fibers, for example monofilaments, films andmoldings, in particular injection molding materials [sic] for electricalor high-temperature-resistant applications. Owing to their high olefinicend group content, they can also be modified by grafting, crosslinkingor other polymer-analogous reactions and can be processed alone or inblends with thermoplastic polymers, rubbers, fillers, etc.

EXAMPLES

Examples 1-8 below illustrate the invention. Their properties are shownin Table 1 in comparison with syndiotactic polystyrene C1.

Tetrakis(4-vinylbenzyl)silane and tetrakis(4-vinylbenzyl)titanium wereobtained by Grignard linking of 4-chloromethylstyrene to silicontetrachloride or to titanium tetrachloride respectively.

The molar masses and molar mass distribution were determined byhigh-temperature GPC at 140° C. with 1,2,4-trichlorobenzene as solvent.The calibration was carried out using polystyrene standards with anarrow molar mass distribution.

The melt viscosity index (MVI) was determined in accordance with DIN 53735 at 290° C., and a weight of 10 kg.

The olefinic end groups were determined by ¹³C-NMR-spectroscopy.

Example 1

3.92 ml (6 mmol) of a solution of methylaluminoxane (MAO) in toluene(1.53 M) from Witco and 0.5 ml (0.5 mmol) of a solution ofdiisobutylaluminum hydride (DIBAH) in cyclohexane (1 M) from Aldrichwere added to 208.3 g (2.0 mol) of styrene and 5.1×10⁻⁵ g (2.0×10⁻⁷ mol)of tetrakis(4-vinylbenzyl)silane in a round-bottomed flask under anitrogen blanket, and the mixture was heated to 60° C. 4.56 mg (2×10⁻⁵mol) of pentamethylcyclopentadienyltrimethyl titanium Cp*Ti(CH₃)₃ werethen added for initiation, and the mixture was polymerized at 60° C. for2 hours. The polymerization was terminated by addition of ethanol, andthe polymer was washed with NaOH/ethanol and dried at 50° C. underreduced pressure.

Examples 2 to 7

Example 1 was repeated with increased proportions oftetrakis(4-vinylbenzyl)silane and thestyrene/tetrakis(4-vinylbenzyl)silane ratios from Table 1.

Comparative example C1

Example 1 was repeated without tetrakis(4-vinylbenzyl)silane.

Example 8

3.92 ml (6 mmol) of a solution of methylaluminoxane (MAO) in toluene(1.53 M) from Witco and 0.5 ml (0.5 mmol) of a solution ofdiisobutylaluminum hydride (DIBAH) in cyclohexane (1 M) from Aldrichwere added to 208.3 g (2.0 mol) of styrene in a round-bottomed flaskunder a nitrogen blanket, and the mixture was heated to 600C. 10.3 mg(2×10⁻⁵ mol) of tetrakis(4-vinylbenzl)titanium were then added forinitiation, and the mixture was polymerized at 60° C. for 2 hours. Thepolymerization was terminated by addition of ethanol, and the polymerwas washed with NaOH/ethanol and dried at 50° C. under reduced pressure.

TABLE 1 Styrene/te- trakis(4-vi- Olefinic nylbenzyl)si- end group Exam-lane molar MVI conc. ple ratio Mw [g/mol] Mw/Mn [ml/10 min] [mol-%] c1 —675 400 2.1 59.3 0.4 1 10⁷/1 1 542 200 1.9 37.4 0.5 2 10⁶/1 3 002 3002.3 42.8 1.1 3 10⁵/1 8 503 400 2.2 74.1 2.7 4 20 000/1 n.b. n.m. 69.45.6 5 10 000/1 n.m. n.m. 95.3 29.3 6 1000/1 n.m. n.m. 124.2 63.3 7 100/1 n.m. n.m. 170.2 — n.m.: not measurable

What is claimed is:
 1. A titanium compound of the formula Ia

where R^(a) is hydrogen, halogen or an inert organic radical having upto 20 carbon atoms, where, in a case where p≧2, the two radicals R^(a)may be identical or different and can, together with the metal atom towhich they are bonded, form a 3- to 8-membered ring, and R^(a) mayfurthermore be a conventional complex ligand; R^(b) is hydrogen,C₁-C₄-alkyl or phenyl; R^(c) is hydrogen, C₁-C₄-alkyl, phenyl, chlorineor an unsaturated hydrocarbon radical having 2 to 6 carbon atoms; n is2-4; m is 0-20; and p is 0-2; with the proviso that the sum n+pcorresponds to the valence of Ti.
 2. A titanium compound of the formulaIb

where R^(b), R^(c) and m are as defined in claim
 1. 3.Tetrakis(4-vinylbenzyl)titanium.